It is common practice to construct heat exchangers with one or more tubes to conduct a working fluid through a long and sometimes tortuous path to obtain heat transfer between the working fluid and the ambient fluid surrounding the tubes. It has been recognized that paths comprising two tubes in parallel impose a smaller pressure drop between the inlet and outlet of the heat exchanger with resulting improvement in system efficiency.
The chief tube designs which have evolved for heat exchanger use are a round tube and a flat or oval tube. The tubes are connected to input and output ports which generally take the form of a round stub pipe or nipple, the connections being perfected by special fittings adapted to the particular heat exchanger design. It is always important that the fittings enhance system integrity. For that reason the fittings must have a high burst pressure when used with high pressure systems.
When a heat exchanger employs round tubes, two parallel paths are accommodated by a fitting formed of a round tube bent in a U-shape to engage the ends of both tubular paths and a tubular tee branch forming the port at the bend of the U. This fitting has been quite successful. On the other hand, when flat or oval tubes are used for parallel paths a design using a U-shaped flat tube for joining the path ends has the weakness that the internal pressure tends to deform the flat tube into a round shape. The consequential strain at the joints results in a low burst pressure of the fitting. It is thus desired to provide a fitting for plural flat tubes having a high burst pressure.